The present invention is directed to a belt tensioner for a transmission belt system and, more specifically, to an improved damper assembly for the belt tensioner and a method for constructing the belt tensioner incorporating the improved damper assembly.
The main purpose of a belt tensioner that automatically responds to fluctuations in the movements of an endless belt is to prolong the life of the belt itself or of engine components such as accessories operating in conjunction with the belt. Such belt tensioners are typically used in/on front-end accessory drives in an automobile engine. A front-end accessory drive often includes pulley sheaves for each accessory the belt is required to power, such as the air conditioner, water pump, fan and alternator. Each of these accessories requires varying amounts of power at various times during operation. These power variations, or torsionals, create a slackening and tightening situation of each span of the belt. The belt tensioner is utilized to absorb these torsionals through use of an internally mounted torsion spring.
Various embodiments of belt tensioners include an arm pivotally mounted to a base housing or spring case, where a torsion spring is operatively coupled between the arm and the base housing so as to force the distal end of the arm against the drive belt and, in turn, to provide sufficient tension force on the drive belt as desired. The size of torsional loads experienced by the drive belt is sometimes large enough to significantly move the arm away from the belt, causing the tension in the belt to be temporarily reduced. This is not favorable above a certain degree and squealing and squeaking of the belt may result. Therefore, typical belt tensioners incorporate damping devices to slow the pivotal movement of the arm.
In the belt tensioners illustrated and described in U.S. Pat. No. 6,575,860 and U.S. Pat. No. 6,206,797 an arm plate was included as a damping mechanism. The arm plate was deflectable or deformable to apply an axial force on other components of the tensioner, referred to herein as a deflection force. In these embodiments, when the arm plate deflection angle is less than the tapered angle of the sheath, the deflection force can only exist at the outer edge of the plate, and conversely when the arm plate deflection angle is greater than the tapered angle of the sheath, the deflection force can only exist at the edge of the plate's inner diameter. In either situation, when the sheath wears the deflection force either moves radially inward or outward, depending on where the force is applied. Since the location of the force is able to vary depending on the amount of deflection angle set during assembly and amount of wear, tensioner damping becomes increasingly difficult to manage.
An improved dampening device for belt tensioners is needed to solve these problems, especially a design where the deflection force does not move locations as the damping assembly wears over the life of the tensioner.